Thermogravimetry Mass Spectrometry Research Articles

Regeneration Process of Ammonia-Absorbed Zirconium Phosphate to Zirconium Phosphate

Zirconium phosphate [Zr(HPO4)2·H2O] absorbs 2 mol(NH3)/mol[Zr(HPO4)2·H2O] with a low equilibrium plateau ammonia concentration of around 1 ppm in water. In this study, in order to investigate the regeneration process of ammonia-absorbed zirconium phosphate [Zr(NH4PO4)2·H2O], Zr(NH4PO4)2·H2O was heat-treated above 353 K under an inert gas. Then, the structures of the heat-treated samples were evaluated using powder X-ray diffraction and thermogravimetry–mass spectrometry measurements. Zr(NH4PO4)2·H2O started to desorb ammonia and the crystal water at 353 K. Then, Zr(NH4PO4)2·H2O was changed to the anhydrous monoammoniate [Zr(NH4PO4)(HPO4)] at 473 K and formed anhydrous zirconium phosphate [Zr(HPO4)2] at 673 K. The anhydrous zirconium phosphate and the anhydrous monoammoniate reabsorbed ammonia in ammonia water. Those initial absorption rates were small compared with Zr(HPO4)2·H2O. The slow kinetics of the anhydrous zirconium phosphate corresponded to the small interlayer distances. The ammonia concentration composition isotherms indicated that the anhydrous zirconium phosphate and anhydrous monoammoniate have a low ammonia equilibrium plateau concentration of around 1 ppm in ammonia water. Zr(NH4PO4)2·H2O is formed from Zr(NH4PO4)(HPO4) by the reabsorption of ammonia and water after 1–10 cycles. We found that zirconium phosphate is an ammonia remover which can be used repeatedly at 473 K.

Research on Thermal Behaviors and NO x Release Properties during Combustion of Sewage Sludge, Sawdust, and Their Blends.

To investigate the thermal behaviors and NOx emission properties during combustion of sewage sludge (SS), sawdust (SD), and their blends (SS5SD5, SS3SD7, and SS1SD9 with SD proportions of 50, 70, and 90 wt %, respectively), tests were conducted using thermogravimetry–mass spectrometry (TG-MS), Fourier transform infrared spectroscopy (FTIR), and a tube furnace in this study. Results indicated that hydrogen in the fuel was mainly released during volatile combustion, and carbon conversion proceeded during the whole combustion process. With the SD proportion increasing, samples exhibited better combustion characteristics. Compared to SD, SS emitted more NOx due to its higher nitrogen content but showed lower conversion ratios from fuel nitrogen to NOx, and the NOx yields decreased significantly with the increase in SD proportion. NOx emissions of higher volatile samples were more sensitive to temperature, and NOx yields of SD and SS1SD9 continued to decrease from 800 to 1000 °C, whereas NOx yields of SS, SS5SD5, and SS3SD7 changed slightly from 800 to 900 °C and decreased significantly from 900 to 1000 °C. Synergistic effects of cocombustion on NOx emission varied with the blending ratio and temperature. SS5SD5 and SS3SD7 always presented a positive NOx reduction performance, and SS1SD9 exhibited opposite NOx reduction effects at different temperatures. Synthetically considering the SS disposal capacity, combustion characteristic, and NOx yield, an SS proportion of around 30% in blends is more recommended in practical applications.

Pyrolysis of waste Fischer-Tropsch wax: An experimental study

To achieve carbon neutrality and optimize China's energy structure, pyrolysis (thermal cracking) was selected to recycle the Waste Fischer-Tropsch wax (WFTW) produced in large quantities from Fischer-Tropsch synthesis plants, which has rich hydrocarbon content and high calorific value. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), thermogravimetry-mass spectrometry (TG-MS), and thermogravimetric-infrared spectroscopy (TG-IR) were used to investigate the pyrolysis characteristics and mechanism of WFTW. The TG and DSC showed that the main pyrolysis temperature range of WFTW was 230–480 °C, and the heating rate affected the temperature range greatly. Theoretically, more than 87% of the calorific value in the WFTW can be recovered as liquid fuels, and the most suitable heating rate was 15 °C/min. TG-MS and TG-IR showed pyrolysis products at different stages to further investigate the pyrolysis process and provide a basis for recycling WFTW. The activation energy calculated by Kissinger method is 215 ± 3 kJ/mol, and the mean apparent activation energy calculated by Starink method is 133 ± 14 kJ/mol, showing a good agreement with Kissinger method at a high conversion rate (70–80%).

Selective leaching of Li from spent LiNi0.8Co0.1Mn0.1O2 cathode material by sulfation roast with NaHSO4‧H2O and water leach

Extensive research efforts have been made in recycling spent lithium-ion batteries; however, there has been little focus on the selective recovery of lithium from spent lithium-ion batteries. In this paper, we report a new process for selective extraction of lithium from spent lithium-ion power batteries by roasting a mixture of LiNi0.8Co0.1Mn0.1O2 and NaHSO4·H2O followed by water leaching. The most suitable conditions included roasting LiNi0.8Co0.1Mn0.1O2:NaHSO4·H2O at 600 °C for 30 min in a mass ratio of 1:1.40, followed by water leaching at 60 °C for 30 min with a liquid/solid ratio of 25:1 (mL/g). Under the optimal conditions, extraction efficiencies of 99.3%, 0.01%, 3.69%, and 3.90% for Li, Mn, Co, and Ni, respectively, were obtained. X-ray diffraction, in situ X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry–differential scanning calorimetry, and thermogravimetry–mass spectrometry were performed to investigate the transformation of Li, Ni, Co, and Mn in the LiNi0.8Co0.1Mn0.1O2–NaHSO4·H2O roasting system. The results demonstrated that the SO3 produced by thermal decomposition of NaHSO4·H2O considerably affected the transformation of Li, Ni, Co, and Mn in the LiNi0.8Co0.1Mn0.1O2. The surface morphology of the roasted samples showed evidence of sintering and agglomeration. The thermodynamic analysis indicated that the roasting reaction is feasible and that the selective extraction of Li can be achieved by controlling the additive ratio of NaHSO4·H2O.

A Simple Method for Quantification of Polyhydroxybutyrate and Polylactic Acid Micro-Bioplastics in Soils by Evolved Gas Analysis.

Conventional plastics are being slowly replaced by biodegradable ones to prevent plastic pollution. However, in the natural environment, the biodegradation of plastics is usually slow or incomplete due to unfavorable conditions and leads to faster micro-bioplastic formation. Many analytical methods were developed to determine microplastics, but micro-bioplastics are still overlooked. This work presents a simple method for determining poly-3-hydroxybutyrate and polylactic acid micro-bioplastics in soil based on the thermogravimetry–mass spectrometry analysis of low molecular gases evolved during pyrolysis. For the method development, model soils containing different soil organic carbon contents were spiked with micro-bioplastics. Specific gaseous pyrolysis products of the analytes were identified, while the ratio of their amounts appeared to be constant above the level of detection of the suggested method. The constant ratio was explained as a lower soil influence on the evolution of the gaseous product, and it was suggested as an additional identification parameter. The advantages of the presented method are no sample pretreatment, presumably no need for an internal standard, low temperature needed for the transfer of gaseous products and the possibility of using its principles with other, cheaper detectors. The method can find application in the verification of biodegradation tests and in the monitoring of soils after the application of biodegradable products.

Quest for the Co-Pyrolysis Behavior of Rice Husk and Cresol Distillation Residue: Interaction, Gas Evolution and Kinetics

With the tremendous prosperity of industry, more and more hazardous waste is discharged from industrial production processes. Cresol distillation residue is a typical industrial hazardous waste that causes severe pollution without proper treatment. Herein, the co-pyrolysis of rice husk and cresol distillation residue was studied using thermogravimetry–mass spectrometry and kinetic studies. The Coats and Redfern method was employed to calculate the activation energy. The results indicated that the pyrolysis process of cresol distillation residue and RH/CDR (Rice Husk and Cresol Distillation Residue) blends can be divided into four stages and three stages for RH. The introduction of RH not only improved the thermo-stability of cresol distillation residue at a low temperature but also reduced the activation energy of the blends. The activation energy was the lowest when the proportion of rice husk in the blend was 60%. The main gaseous pyrolysis products included CH4, H2O, C2H2, CO2, C3H6 and H2. There existed an unusual combination of synergistic and inhibitive interactions between RH and cresol distillation residue, respectively, within different temperature ranges. The synergistic interaction decreased the reaction’s activation energy, whereas the inhibitive interaction reduced the emission of main gaseous products, such as CH4 and CO2. It was concluded that the addition of RH was conducive to improving the pyrolytic performance of cresol distillation residue and the resource utilization of cresol distillation residue.

Investigation into the interaction of biomass waste with industrial solid waste during co-pyrolysis and the synergetic effect of its char gasification

In this work, the interaction between waste cypress sawdust (WCS) and coal liquefaction residue (CLR), a type of industrial solid waste, during co-pyrolysis was studied by thermogravimetry-mass spectrometry (TG-MS) and pyrolysis-gas chromatography mass spectrometry (Py-GC/MS). The gasification reaction characteristics of co-pyrolysis char were also evaluated. The results showed that both promoting and inhibiting effects existed in the co-pyrolysis process of WCS and CLR. When the pyrolysis temperature was less than 420 °C, the catalysis of minerals was conducive to the pyrolysis reaction. At higher temperatures, the polycondensation and carbonization produced by the interaction between the components inhibited the release of volatiles. The gasification reactivity of co-pyrolysis char was better than that of individual WCS and CLR chars. The synergistic effect was most obvious when the blending ratio of WCS to CLR was 3:1. In the gasification process of co-pyrolysis char, the WCS component with better reactivity preferentially reacted to form an abundant pore structure, which exposed more reactive sites and promoted the diffusion and mass transfer of gasification agent. Moreover, alkali and alkaline earth metal species in WCS and iron bearing minerals in CLR can catalyze the gasification reaction, contributing to the synergistic effect. Therefore, the addition of a suitable solid waste to biomass waste can improve the energy efficiency and simultaneously achieve solid waste utilization.

Insights Into the Properties of Amygdalin Solvatomorphs: X-ray Structures, Intermolecular Interactions, and Transformations.

Amygdalin is an effective component of the traditional Chinese medicine bitter almond, peach kernel, and plum kernel. It has pharmacological effects, such as relieving cough and asthma. In a study of the crystallization process, we found a series of solvatomorphs of amygdalin (including hydrate). Interestingly, in the structures of these solvatomorphs, the same characteristic structural fragment is present, that is, amygdalin dihydrate. Multiple analytical techniques were used to characterize the solvatomorphs, such as X-ray diffraction and thermogravimetry–mass spectrometry. Void calculations of water and solvent were used to analyze the occupied volume in the unit cell of the corresponding solvatomorphs to explain the formation mechanism of the solvatomorphs from the perspective of space. To elucidate the formation mechanism of the solvatomorphs with this kind of characteristic structure from the perspective of energy, theoretical calculations based on density functional theory were applied, such as energy decomposition and molecular electrostatic potential surfaces. In addition, the transformation phenomenon between these solvatomorphs and amygdalin was identified, and the transformation pathways are described in detail.

Comparison of Pyrolysis and Combustion Processes of Vinyl Floor Panels Using Thermogravimetric Analysis (TG-FTIR) in Terms of the Circular Economy

The article analyzes the thermal degradation in the inert and oxidative atmosphere of waste vinyl panels, the main component of which is PVC. Both pyrolysis and incineration of plastic waste are difficult, complex and multifaceted processes due to several physical and chemical phenomena occurring during their performance. The coupled TG-MS (thermogravimetry-mass spectrometry) analysis combined with the Fourier transform infrared spectrometry (TG-FTIR) analysis was used to identify the decomposition mechanisms of waste vinyl panels. Thermogravimetric tests were carried out for two heating rates of 5 and 20 K/min in the temperature range of 40–1000 °C, mass losses were determined, and products resulting from thermal degradation were identified. It was found that the individual components decompose at different temperatures depending on the heating rate and the choice of an inert or oxidative atmosphere. Vinyl floor panels were treated in terms of secondary raw material, which, in the light of the circular economy, may constitute a potential energy or chemical resource.

Evolution of Black Talc upon Thermal Treatment

Black talc is a natural silicate clay mineral with a typical 2:1 layered structure, low electrical conductivity, large specific surface area, and high thermal stability. The world’s largest black talc mine, with known reserves of one billion tons, is located in China’s Jiangxi province. Due to the restriction of its color, the application of black talc is only limited to ceramic raw materials, coating filler, waterproof materials, and other low-end application industries. Thermal treatment is a common method of clay mineral modification. It is vital to examine the structural and physical changes of black talc during calcination in order to prepare black-talc-based composites and to broaden their applications. This work discusses the evolution of black talc upon thermal treatment (30–1000 °C) and the corresponding structural changes. The thermal stability of minerals was analyzed via thermogravimetric (TG) analysis and thermogravimetry–mass spectrometry (TG-MS). The decomposition of minerals during calcination consists of four processes: dehydration, organic carbon decomposition, dihydroxylation, and phase transformation. In situ FTIR and in situ XRD were employed to track changes in black talc in real time during thermal treatment. At 800 °C, black talc was found to begin to go through dihydroxylation, and the crystallinity index decreased significantly. The XRD pattern of samples at 950 °C (T950) showed the reflection of the enstatite structure, and the relative crystallinity index was 27.3%, indicating that the mineral had undergone phase transformation. In addition, the Brunauer–Emmet–Teller (BET), laser particle size analyzer, Zeta potential, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques were used to systematically characterize the physicochemical properties of minerals at different temperatures. The results show that black talc’s particle size and specific surface area increase with the calcination temperature. The surface charge changes, and more amorphous SiO2 and MgO appear, indicating that thermal treatment could induce structural changes and activate the surface of black talc.

Mercury release behaviors of Guizhou bituminous coal during co-pyrolysis: Influence of chlorella

Co-pyrolysis of coal and seaweed can not only effectively decrease the carbon footprint but also improve the quality and output of coal pyrolysis products, however, the influence of seaweed on thermal releasing behaviors of mercury during co-pyrolysis process are still unclear. In this work, the chlorella and Guizhou bituminous coal were mixed and used to reveal the mercury release behavior during co-pyrolysis by the temperature programmed pyrolysis experiments, thermogravimetric and differential thermogravimetric analysis (TG-DTG) and thermogravimetry-mass spectrometry (TG-MS) methods, offering a sufficient explanation on the control technology of mercury pollutants in co-pyrolysis. The results exhibited that a large amount of reducing gases such as CO, H2 and H2O were generated in chlorella at the temperature range of 100-500°C, which was favorable for the transformation from oxidized mercury to elemental mercury, thus remarkably increased the release of elemental mercury in the raw coal sample. The mixed chlorella also significantly lowered the decomposition temperature range (from 400-600 to 300-400°C) of pyrite-bound mercury and decreased the decomposition temperatures of the pyrite-bound mercury species. Additionally, in the co-pyrolysis about 91.82% of mercury was released into the gas phase below 400°C and was 13.77% higher than that of in individual pyrolysis of coal.

Curing mechanism of resole phenolic resin based on variable temperature FTIR spectra and thermogravimetry-mass spectrometry

To solve the problem that the curing mechanism evolution of phenolic resin catalyzed by Ba(OH)2 remained unclear, the p-p methylene index, o-p methylene index, o-o methylene index, hydroxymethyl index, and ether index were introduced to quantitatively investigate the chemical structure of resin in the curing temperature range of 90–230°C. The chemical structures were investigated by variable temperature FT-IR. The gas products released with the increase of curing temperature were characterized by Thermogravimetry-Mass Spectrometry. The curing mechanism from 90°C to 230°C was concluded finally. The results show that the main reaction is the formation of the p-p methylene group in the range of 90–120°C. It is difficult to form the o-p methylene bridge at this stage. In the range of 120–160°C, the main reaction is the formation of the p-p methylene group. From 160°C to 190°C, the main reactions are the breaking of the ether bond, the formation of the carbonyl group and the propyl bridge. Above 190°C, the main reactions are polycondensation reaction among phenolic hydroxyl groups, and the formation reaction of carbonyl groups. The ether bond breaks completely above 230°C. This work provides a new method to investigate the curing mechanism. It is a benefit for the rational design of the curing process of phenolic resin-based composites.

Quantifying the removal of stabilizing thiolates from gold nanoparticles on different carbon supports and the effect on their electrochemical properties.

Gold nanoparticles <10 nm in size are typically prepared using stabilizing agents, e.g. thiolates. Often standard recipes from literature are used to presumably remove these stabilisers to liberate the surface, e.g. for catalytic or electrocatalytic applications, however the success of these procedures is often not verified. In this work, thiolate-stabilised AuNPs of ca. 2 nm in size were synthesized and supported onto three different carbon supports, resulting in loadings from 15 to 25 wt% Au. These materials were post treated using three different methods in varying gas atmospheres to remove the stabilizing agent and to liberate the surface for electrochemical applications. Using thermogravimetry - mass spectroscopy (TG-MS), the amount of removed stabilizer was determined to be up to 95%. Identical location scanning transmission electron microscopy (il-(S)TEM) measurments revealed moderate particle growth but a stable support during the treatments, the latter was also confirmed by Raman spectroscopy. All treatments significantly improved the electrochemically accessible gold surface. In general, the results presented here point out the importance of quantitatively verifying the success of any catalyst post treatment with the aim of stabilizer removal.

Improvement of the leach efficiency of carbonaceous gold concentrates using reduction roasting pretreatment technology

Carbonaceous gold concentrates were pretreated using a reduction roasting method. The roasting process was investigated by thermogravimetry-mass spectrometry and X-ray diffraction. The characteristics of the thermal reaction process and gas release, and the removal mechanism for pyrite and organic carbon were analyzed. Results showed that the thermal decomposition and reduction reactions caused the highest weight loss. The main gold-locked mineral of pyrite was eliminated by decomposition and reduction reaction to produce FeS and S2. The “preg-robbing” ability of organic carbon was eliminated by thermal decomposition to converted into graphite. After reduction roasting, exposed gold content increased from 34.65% to 83.25%, organic carbon removal rate was 98.38%, and the gold leaching rate increased significantly from 2.43% to 73.7%. The technology solved the gold locking and “preg-robbing” problems of organic carbon, prevented the production of SO2, which realized a highly efficient and clean pretreatment for carbonaceous gold concentrates.

In situ synthesis and catalytic decomposition mechanism of CuFe2O4/g-C3N4 nanocomposite on AP and RDX

In order to develop a usable low-cost nanocomposite with better catalytic performances for solid propellants, the CuFe2O4/g-C3N4 nanocomposite commonly used in photocatalysis was first used as combustion catalysis. CuFe2O4/g-C3N4 nanocomposite was designed and successfully prepared by in situ solvothermal method. And the synergistic effect of CuFe2O4 nanoparticles and g-C3N4 on the thermal decomposition of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and ammonium perchlorate (AP) and their catalytic decomposition mechanisms were analyzed systematically. The results indicate that g-C3N4-based combustion catalyst exhibits better catalytic decomposition effect on AP and RDX compared to bulk g-C3N4 and related GO-based catalysts (CuFe2O4/GO). CuFe2O4/g-C3N4 nanocomposites shift the decomposition of RDX to a lower temperature with the increase of g-C3N4 content, while present the opposite trend for AP. Besides, the thermal decomposition stages and related products of AP and RDX probed by thermogravimetry-mass spectrometry (TG-MS) reveal that CuFe2O4/g-C3N4 catalyst reduces their decomposition temperatures, changes their decomposition processes and presents a better catalytic decomposition effect on AP and RDX. Thus, nano g-C3N4-based metal composite oxides used as combustion catalysts will be a more viable strategy in the field of solid propellants.

Cellulose gasification with Ca–Fe oxygen carrier in chemical-looping process

Biomass-derived chemical looping gasification (BCLG) is a novel technology for lignocellulose energy applications. Ca–Fe oxygen carriers have been proven to be a potential material for efficient lignocellulose conversion and hydrogen-enriched syngas production in process studies. In this study, Thermogravimetry-mass spectrometry (TG-MS), pyrolysis chromatography-mass spectrometry (Py-GC-MS) and fixed-bed experiments were conducted, and the cellulose BCLG product was analyzed to explore the mechanism of reaction between Ca–Fe OCs and biomass char or volatiles. The mechanism of the synergistic effect of Ca–Fe was analyzed to explain the characteristics of the OCs. The results suggest the Ca-based materials act as catalysts to promote the decomposition of cellulose monomers at primary reaction and char at secondary reaction, and also promote the reforming and oxidation of volatiles by chemisorption. Ca participates in the construction of inert substances, such as Ca2Fe2O5, to avoid the deep oxidation of CO and H2. Fe-based material supplies oxygen and promotes the reforming of volatile. Compared with Fe2O3 and CaO/Fe2O3, CaFe2O4 shows a better performance on carbon conversion and H2 production below 850 °C.

LiN5: A novel pentazolate salt with high nitrogen content

A high energy cyclo-pentazolate (cyclo-N5−) salt with 90.98 % nitrogen content, LiN5, was synthesized by a simple metathesis reaction of AgN5 and LiCl in deionized water. It was characterized by 15N nuclear magnetic resonance, infrared and Raman spectroscopy, elemental analysis, thermogravimetry-mass (TG-MS) spectrometry, and differential scanning calorimetry. Besides, its trihydrate (LiN5·3H2O) and anhydrous zeolitic architecture (LPF, lithium-pentazolate framework) structures were confirmed by single-crystal X-ray diffraction. LiN5 achieved stability in air and under ambient conditions. It starts to decompose when heated to 133 °C (onset) under Ar2 flow. Its relatively high density (1.75 g cm−3), impact and friction sensitivity (IS = 3 J; FS = 20 N), and calculated high heat of formation (3.44 kJ g−1), combined with its theorical superior detonation velocity and pressure (D = 11362 m s−1, P = 40.9 GPa), endow LiN5 with potential as an environmentally primary explosive.

Improved thermal stability and heat-aging resistance of silicone rubber via incorporation of UiO-66-NH2

The metal-organic frameworks (MOFs) as emerging materials have attracted worldwide attention. In this study, a novel strategy by blending classic MOFs material UiO-66-NH2 to efficiently enhance the thermal stability and thermal aging resistance of silicone rubber (SR) was proposed. The experimental results indicated that very low dosage (0.25–1.5 part) of UiO-66-NH2 addition could effectively increase the thermal-oxidative stability of SR, which was proved by that the values of T5 (temperature at 5% weight loss) and Tm (the maximum thermal decomposition rate temperature) of SR were greatly increased by 43.4 °C and 97.9 °C, respectively. Moreover, the retention rate of elongation at break and tensile strength of SR with 1.5 part UiO-66-NH2 could remain about 72% and 57% after 288 h treatment in 210 °C. The possible heat resistance mechanism was explored by processing torque (PT) and thermogravimetry-mass spectrometry (TG-MS), whose results suggested that even very low addition of UiO-66-NH2 could efficiently inhibit degradation of SR chains and obstruct heat transfer due to its low thermal conductivity. This study provided a novel strategy to enhance thermal stability of rubber materials, and might open up new filed for polymer material processing.

Co-pyrolysis of waste polyvinyl chloride and oil-based drilling cuttings: Pyrolysis process and product characteristics analysis

Oil-based drill cuttings (OBDC) and waste polyvinyl chloride (waste PVC) both are solid wastes. The pyrolysis/co-pyrolysis characterizations of OBDC, waste PVC and OBDC/waste PVC at varying heating rates were investigated using thermogravimetric analysis (TG/TGA). Coats-Redfern and Kissinger integration methods were employed to fit the TG curve. The optimal fitting effect was obtained with reaction order at 2 and Kissinger integration method was better than Coats-Redfern integration method for co-pyrolysis of OBDC/waste PVC. The practical co-pyrolysis condition was optimized using batch experiment and the optimal condition was as following: final temperature for 600 °C, holding time for 60 min, heating rate at 10 °C/min and ratio of PVC as 10% PO. The gas, solid and liquid phase products of pyrolysis/co-pyrolysis were characterized and analyzed using thermogravimetry-mass spectrometry (TG-MS), gas chromatography-mass spectrometry (GC-MS) and X-ray diffraction (XRD). The gas product of pyrolysis/co-pyrolysis indicated the inhibitory effect on HCl emission due to the positive synergic effect of OBDC and PVC. High pyrolysis temperature was beneficial to increase the content of hydrocarbons, which enhanced the quality of oil recovery. This study indicated that the co-pyrolysis of OBDC and waste PVC is a promising method for waste disposal and oil recovery.

Formation of ZrC-SiC Composites from the Molecular Scale through the Synthesis of Multielement Polymers.

In the field of non-oxide ceramic composites, and by using the polymer-derived ceramic route, understanding the relationship between the thermal behaviour of the preceramic polymers and their structure, leading to the mechanisms involved, is crucial. To investigate the role of Zr on the fabrication of ZrC–SiC composites, linear or hyperbranched polycarbosilanes and polyzirconocarbosilanes were synthesised through either “click-chemistry” or hydrosilylation reactions. Then, the thermal behaviours of these polymeric structures were considered, notably to understand the impact of Zr on the thermal path going to the composites. The inorganic materials were characterised by thermogravimetry-mass spectrometry (TG-MS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). To link the macromolecular structure to the organisation involved during the ceramisation process, eight temperature domains were highlighted on the TG analyses, and a four-step mechanism was proposed for the polymers synthesised by a hydrosilylation reaction, as they displayed better ceramic yields. Globally, the introduction of Zr in the polymer had several effects on the temperature fragmentation mechanisms of the organometallic polymeric structures: (i) instead of stepwise mass losses, continuous fragment release prevailed; (ii) the stability of preceramic polymers was impacted, with relatively good ceramic yields; (iii) it modulated the chemical composition of the generated composites as it led, inter alia, to the consumption of free carbon.